Muchuu ni Naru yo

Towa and Yamato are twins with very different personalities. Yamato is loud, outgoing, and regularly gets into fights, while Towa is quiet, studious, and always suffering the after effects of Yamato's actions because he's always being mistaken for his brother.
On his way home from school one day, Towa was getting beaten up by the school gang who had mistaken him for Yamato, when he met Mitsuru, a mysterious delinquent. For some reason, Mitsuru can tell the twins apart...